When comparing Yahoo! Mail vs Postbox, the Slant community recommends Postbox for most people. In the question“What are the best e-mail clients for Windows?” Postbox is ranked 6th while Yahoo! Mail is ranked 12th. The most important reason people chose Postbox is:
All messages in one place. But you can select to show only messages from each account either.
Specs
Question Ranking
Pros
Pro Tabs
With this Yahoo! Mail feature users can open any e-mail in a new tab and get back to the mail list without having to close the e-mail that the user is currently reading.
Pro Stationary
Stationary is an add-on that's only available in Yahoo! Mail. It allows users to customize and enhance the look of the email. Things like image borders, letter style etc. can be changed before sending the email to intended recipients.
Pro Background wallpaper
Similar to Mail app bundled in Windows 10, Yahoo! Mail allows users to set images from Flickr as the background image for the app.
Pro One Inbox for all accounts
All messages in one place. But you can select to show only messages from each account either.
Pro Quick Bar for macros
Quick bar allows you to add a variety of content to your message. It will let you reuse URLS in your Sent folder, and autocompletes against canned responses, signatures, and topics.
Cons
Con Only supports Yahoo! Mail
Because it's a mail app developed by Yahoo!'s, it only supports Yahoo! Mail accounts.
Con Way too expensive
Currently the price is at 45€. That's ridiculous for an E-Mail client. The design alone is pretty but neither does that or the functionality in any way justify the pricing.